This invention relates to a process for the manufacture of 1,4-bis(4-phenoxybenzoyl)benzene in a homogeneous or heterogeneous system, in the presence of certain metal salt catalysts.
1,4-Bis(4-phenoxybenzoyl)benzene (sometimes referred to hereinafter as BPBB) which is an important intermediate in the manufacture of polyetherketone resins, is currently made industrially by a reaction of 1,4-benzenedicarbonyl chloride with diphenyl ether in the presence of a Friedel-Crafts catalyst, usually aluminum chloride, which is employed in an amount of at least three moles per mole of 1,4-benzenedicarbonyl chloride. Polyetherketones are a well known generic class of commercial resins, which include polyetherketones proper, poly(ether ether ketones), poly(ether ketone ketones), and mixed copolymers having segments of both the first named type and the last named type. Diphenyl ether normally is used in a significant excess to minimize formation of higher oligomers. Normally, the reaction is carried out in a solvent such as, e.g., 1,2-dichlorobenzene, at a temperature of approximately 0.degree. C. After the reaction is complete, methanol is added to precipitate the product and remove the catalyst therefrom. The product is filtered off, washed repeatedly with methanol, and recrystallized from N,N-dimethylacetamide or 1,2-dichlorobenzene.
The use of aluminum chloride presents various shortcomings. The recovered aluminum chloride cannot be reused and this creates a waste disposal problem as well as adds to the cost of the operation. Further, aluminum chloride does not have a high para,para-isomer selectivity, so that it tends to also produce a fair proportion of the ortho,para-isomer, i.e., [1-(2-phenoxy),4-(4-phenoxy)]dibenzoylbenzene. Because of extensive purification, requiring repeated filtrations, long recovery times are needed.
BPBB can also be manufactured by a reaction of 1,4-benzenedicarbonyl chloride with excess diphenyl ether at 190.degree.-258.degree. C. in the presence of hydrogen-exchanged zeolite catalysts, which are highly para,para-isomer selective, as taught in the copending application of Corbin et al., Ser. No. 07/218941, filed July 14, 1988, and now allowed. While the invention disclosed and claimed in that allowed application represents a considerable advantage over the above-described current industrial process, it too has certain drawbacks. It requires a very large excess of diphenyl ether as well as a significant amount of zeolite catalyst. The high ratio of diphenyl ether to 1,4-benzenedicarbonyl chloride and the large amount of catalyst make the operation quite costly. Further, the hydrogen-exchanged zeolite must be either regenerated or disposed of, which again increases the manufacturing cost.
It is, therefore, desirable to be able to produce BPBB in an isomer-selective, simple operation, requiring no solvent, run with a smaller excess of diphenyl ether, and with a significantly smaller amount of catalyst. It further would be highly desirable to be able either to reuse the catalyst without regeneration or to dispose of it without major expense.